1. Field of the Invention
The present invention relates to a projection type display apparatus using a rod type integrator having a rod to internally reflect light entering an entrance face and emit the light from an exit face thereof.
2. Description of the Related Art
A projection type display apparatus is known such as a projector to project, onto a screen, images formed by an electro-optical device such as a liquid crystal panel or a DMD (digital micro-mirror device) on the basis of image data from a personal computer, a video camera or the like. In this kind of projection type display apparatus, a rod type integrator system is known as a means to provide uniform illuminance distribution of an emitted light beam. In such system, light entering one end face, as an entrance face, of a rod such as a glass rod is internally reflected within the rod, and is emitted from an exit face thereof. The effect of the rod type integrator increases or decreases depending on number of internal reflections within the rod, F value of a light source, and so on. It is known as being effective to reduce the cross section of the rod and to increase the length of the rod as well as to set the F value of the light source to a low value.
It is easy for this rod type integrator system to heighten parallelism of illumination light and to be adapted to miniaturization of electro-optical devices such as liquid crystal panels. Examples of rods to be used for the rod type integrator are a solid rod such as being made of glass, and a hollow rod such as having an internal surface made of mirror surface. It is known that the solid rod e.g. of glass can use light more efficiently than the hollow rod, since the surface of the internal reflection in the case of the solid rod can have a reflectivity of nearly 100%.
In the case of the solid rod, however, if a portion of side surface thereof is contaminated with dirt or damaged, the total reflection condition in the rod is corrupted, thereby causing light leakage at such portion. This causes a problem that the light use efficiency decreases. Furthermore, optical components such as a condenser lens are interposed between the exit face of the rod and the electro-optical device such as a liquid crystal panel, so that the exit face of the rod and the electro-optical device are conjugate with respect to the optical components. Accordingly, if e.g. dust is deposited on the exit face of the rod, an image containing an image of the dust being deposited is formed at the position of the electro-optical device, and is thus formed on the screen as well.
For solving such problem, it is known to cover the side surface of the solid rod with a cover member made of a tubular body, and further to provide transparent member(s) on the entrance face and/or the exit face of the solid rod. (Refer to Japanese Laid-open Patent Publication 2001-228541.) In the case of this known technology, e.g. incoming dust to deposit on the side surface of the rod can be reduced, since the side surface of the solid rod is covered with the cover member.
It is described in the above-referred Patent Publication that because of the provision of the transparent member on the exit face of the rod, no images of e.g. dust are formed on a liquid crystal panel, which is conjugate with the exit face of the rod, and hence that images of e.g. dust are prevented from being formed on the screen. It is further described therein that because e.g. dust can be prevented from incoming and depositing on the side surface of the rod, it becomes possible to increase the light use efficiency.
However, according to the apparatus described in the above-referred Patent Publication, the solid rod is fixed to the cover member using a screw, although it is described therein to so hold the solid rod as to reduce its contact with the cover member as much as possible. Accordingly, light leakage still occurs at a portion of the solid rod where the screw makes a point contact thereby causing light use efficiency to decrease. In the case of the configuration as shown in FIG. 6 of the above-referred Patent Publication, in particular, the exit end face of the solid rod is positioned at a space in the cover member. Accordingly, e.g. dust generated at the time of tightening the screw may deposit on the exit end face of the solid rod, thereby causing images of e.g. the dust to be formed at the position of the electro-optical device, and thus deteriorating projected images.
In the case of the configuration as shown in FIG. 8 of the above-referred Patent Publication, a condenser lens is attached to the exit end face of the solid rod. However, since such end face is a face to function as a focal plane, it is disadvantageous that the condenser lens is attached to such end surface. Further, in the case of the configuration as shown in FIG. 12 of the above-referred Patent Publication, a condenser lens is attached to an exit end face of a hollow rod (light tunnel). In such case, the focal plane at the exit thereof is positioned at a position inner than the end face of the hollow rod, whereby an end portion of the hollow rod from the end face thereof to the focal plane at the exit thereof becomes a useless portion.
Moreover, in the above-referred Patent Publication, a holding unit having a rectangular shape is used. Accordingly, it is not easy to adjust the relative positions of the solid rod or the hollow rod with the optical components placed in front of and behind such rod in the direction of the axis of such rod. In particular, it is not easy therein to adjust centering of such elements. Furthermore, since the rod is covered with the cover member, there is a problem particularly in the case of the solid rod which is likely to be easily heated by a light beam to an overheat condition, such that it is difficult to sufficiently cool the solid rod in its entirety.